Stephen d



(No Model.)

S. D. FIELD.

, UNDERGROUND TELEGRAPH-SYSTEM. No. 291,317. Patented Jan. 1, 1884.

WITNESSES INVENTOR a I {7, r M By hi6 flltomeys Stephen 12.11am

@M 6%,7MJMS.

STEPHEN D. FIELD, OF NEIV YGRK, X. Y.

UNDERGROUND TELEGRAPH SYSTEM.

SPECIFICATION forming part of Letters Patent No. 291,317, dated January 1, 1584. Application filed May 5, 1883. (N0 model.)

To aZZ whom, it may concern:

Be it known that I, Srnrnnn D. FIELD, a citizen of the United States, and a resident of the city, county, and State of N ew York, have invented certain new and useful Improvements in Underground Telegraph Systems, of which the following is a specification.

My invention relates to systems for convey ing and distributing electrical conductors uir der ground.

The object of my invention is to prevent the destruction of the insulating material incasing the conductors, both from the action of the electrical current itself in overheating the insulating material and from the action of moisture, which not only serves to destroy the insulation, but which is itself a conducting medium by which the current escapes to ground.

My invention consists in a mode of protect ing the insulation of underground conductors, which consists in maintaining (preferably in circulation) within the conduits containing the conductors one or other of the gases which do not support combustionsuch, for example, as carbonic-acid gas or air from which the oxygen has been removed. This gas is to be applied in a dry state, and preferably to be maintained in circulation within the conduits.

This invention constitutes an improvement upon the system described in Letters Patent No. 238,492, granted to me October 19, 1880, and entitled Improvement in Underground Telegraphs. described a means for causing the circulation of dry air within the conduits of an underground system for the sole purpose of absorbing the moisture.

I now propose to substitute for the dry air a gas or vapor, which has, in addition to the property of absorbing moisture, the advantage of being a non-supporter of combustion.

It is well known that all electrical currents develop more or less heat in the circuit of conductors which they traverse. At points of high electrical resistance the heat is often sufficiently developed to cause the burning of the insulating material. This action, while primarily due to the current, is greatly aided by the oxygen of the atmosphere, which frequently continues to support the combustion There was therein shown and at the heated point until this insulation has been completely destroyed. \Vith the proposed gas this difficulty is overcome.

My invention is set forth in the accompanying drawing, in which is shown a closed system of conduits, A A, which is made as nearly air-tight as possible. The conductors B may be disposed in this conduit in any convenient manner. At one end is an apparatus, G, for generating or supplying the dry carbonic-acid gas or other non-supporter of combustion. This apparatus may be of any convenient iormas, for example, a retort or pressuretank. If desired, the carbonic-acid gas maybe generated as required by the burning of charcoal or in other equivalent ways. At the other end of the conduit system may be placed an exhausting apparatus, D, which may also be of any convenient formsuch, for example, as that shown and described in the above-mentioned Letters Pateutits office being to maintain a circulation throughout the conduit system of the gas furnished at O; or this apparatus may be dispensed with and the gas caused to travel through the system by virtue of its own pressure.

I am aware that in the Letters Patent alluded to above means are shown for maintaining a circulation of the dry air; but 1nyinvention consists in the application of a new agent in the place of the dry air, and is independent of the particular means employed to maintain the same in motion.

' I claim as my invention 1. The combination, substantially as hereinbcfore set forth, of the insulated electrical conductors, the sealed conduit, within which said conductors are disposed, and the dry carbonic-acid gas therein maintained.

2. The mode described of preventing the combustion of the insulating material of elec trical conductors, which consists in placing them in conduits within which dry carbonicacid gas is maintained.

In testimony whereof I have hereunto subscribed my name this 2d day of May, A. D. 1883.

STEPHEX D. FIELD.

Witnesses:

DANIEL W. Enenconn, CARRIE E. DAVIDSON. 

